Good morning all. I've been working on a 292 with a 3x2 intake for several years now. I've gotten to a point where I can drive the vehicle for short trips, but I'm intermittently getting a backfire under acceleration once the engine warms up. Its also cut off on me twice at a stop. I think it might have been vapor lock, because it restarted pretty quickly. Ive sent the carbs out to be professionally rebuilt. I called the cam manufacturer and my initial timing is where it should be. (10⁰ btdc) I've been trying to do some research about what else might be causing my concern. I'm wondering if I'm getting an issue from the heat riser ports running under my center carb. I'm using the wide open gaskets, not the truck ones with the smaller opening. Could this be my issue? I'm trying to make the power tour this year and I'm running out of time. Any help would be appreciated. Cam is an isky 301333, Weiand intake. 292 bored .090 over. Red's headers that have been ceramic coated to lower under hood temps, gasket-match porting on a set of G heads.

Ditto on the comments about ethanol laden fuel running leaner.  I typically have to add a couple of jet numbers to the jetting to compensate for 5-10% ethanol fuel.

I have had a couple of Ford Y 3X2 setups recently in the shop with the Ford/Holley 2V carbs that had been ‘professionally’ set up elsewhere.  Both setups initially ran extremely lean when dyno testing them as delivered.  Upon disassembling the carbs, I found that the end carburetor power valves had been removed but the end carb jetting had also been further reduced from the stock numbers.  On both of those 3X2 set ups, the primary jetting was #55 and the secondary (end carbs) was #53.  In the grand scheme of things, when blocking the power valves, jetting should be increased, not decreased. 

On the last one I ran, I bumped the jetting up to 59P and 60S and immediately saw a plus thirty horsepower improvement along with the lean popping during load being reduced so I knew I was on the right track.  I ended up with 59P and 67S jetting and the engine both idled and throttled up well.  This particular engine had an Isky E4 camshaft so nothing wild in that department.

Lorena, Texas (South of Waco)

Vintage speed has adjustable main jets $39.99 a pair
i did not see any larger main jet then 60 

I'll go ahead and order the spacers. I'm going to pick up a infrared thermometer to get a reading on the temps around the fuel lines. I try to use non ethanol fuel when I can, but I won't be able to guarantee that I can find it on long trips. I'll check the jets, but I want to say they're something like 51s and 48s. Does anyone have any dealings with Charlie Price?

Also, could I expect to need similar sized jets? I'm in NC, so we're basically at sea level.

While it has not been clarified exactly what carburetors are being used, the Ford/Holley 3 bolt 2V carbs do use the conventional Holley jets which are available in most sizes up to ‘100’ through many different parts suppliers including Speedway, Jegs, and Summit.  The Stromberg carbs on the other hand use main jets that are specific to the Stromberg carbs and slightly more difficult to find when looking for specific sizes.

Lorena, Texas (South of Waco)

This is an afterthought, but would this Weiand manifold happen to be made for the '54 239 and 256 engines?  If so, intake gasket sealing would be very iffy with G heads.  Likely cause vacuum leak.

John - "The Hoosier Hurricane"

I will get the part number off of the intake when I get back to the house. The carbs are holley 94s. 1 1/16" venturi on the center and 1" on the secondary carbs

Intake is the Weiand FM 436

Jets were 56P and 50S